Questions raised by the consumption of cane sugar by a Black-throated Blue Warbler (<em>Setophaga caerulescens</em>)

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Gary R. Graves

Abstract: I address questions raised by an observation of a Black-throated Blue Warbler (Setophaga caerulescens) eating un- refined granulated cane sugar in Kingston, Jamaica. Sugar consumption implies the presence of taste receptors sensitive to sucrose and digestive sucrase activity sufficient to assimilate highly concentrated sucrose solutions. The ability to efficiently di- gest disaccharides, such as sucrose, and more complex oligosaccharides has permitted wood warblers and other nine-primaried oscines to exploit nectars of hummingbird-pollinated flowers and homopteran honeydew that may not be easily digested by avian clades such as thrushes and mimids that appear to lack digestive sucrases. In a broader context, clade-specific differences in digestive physiology may result in resource use patterns in birds that mimic the outcome of interspecific competition.

Keywords: Black-throated Blue Warbler, cane sugar, digestive enzymes, interspecific competition, Jamaica, nectarivory, saccharides, Setophaga caerulescens, sucrase, sucrose

Resumen: Cuestiones planteadas por el consumo de azúcar de caña por Setophaga caerulescens—Aquí abordo preguntas surgidas por la observación de Setophaga caerulescens alimentándose de azúcar de caña granulada y sin refinar en Kingston, Jamaica. El consumo de azúcar implica la presencia de receptores de gusto sensibles a la sacarosa así como suficiente actividad digestiva de sacarasa para asimilar soluciones altamente concentradas de sacarosa. La habilidad para digerir eficientemente los discáridos, tales como la sacarosa, y oligosacáridos más complejos ha permitido a los parúlidos y otros oscines con nueve primarias aprovechar néctares de flores polinizadas por colibríes y la melaza producida por homópteros que pueden no ser fácil- mente digeridos por clados de aves como túrdidos y mímidos que carecen de sacarasas digestivas. En un contexto más amplio, las diferencias clado-específicas en la fisiología digestiva pueden resultar en patrones de uso de recursos en aves que imiten el resultado de la competencia interespecífica.

Palabras clave: azúcar de caña, competencia interespecífica, enzimas digestivas, Jamaica, nectivoría, sacarasa, sacáridos, sacarosa, Setophaga caerulescens

Résumé: Questions soulevées par la consommation de sucre de canne par une Paruline bleue (Setophaga caerulescens)—Sont traitées ici les questions soulevées par l’observation d’une Paruline bleue (Setophaga caerulescens) se nourrissant de sucre de canne cristallisé non raffiné à Kingston, en Jamaïque. La consommation de sucre implique la présence de récepteurs du goût sensibles au saccharose, et d’une activité de digestion par la sucrase suffisante pour assimiler des solutions très concentrées en saccharose. La capacité à digérer efficacement les disaccharides tels que le saccharose, et les oligosaccharides plus complexes, a permis aux parulines et autres espèces du groupe des oscines pourvues de 9 rémiges primaires d’exploiter le nectar des fleurs pollinisées par les colibris et le miellat des homoptères, qui ne peuvent pas être facilement digérés par les clades tels que les grives et les mimidés qui semblent manquer de sucrases digestives. Dans un contexte plus large, les différences spécifiques des clades dans la physiologie digestive peuvent aboutir à des modèles d’utilisation des ressources par l’avifaune qui imitent les résultats de la compétition interspécifique.

Mots-clés: compétition interspécifique, enzymes digestives, espèces nectarivores, Jamaïque, Paruline bleue, saccharides, saccharose, Setophaga caerulescens, sucrase, sucre de canne

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